Using the paranoia gem when joining tables
Something I learned today about joining two tables that both use acts_as_paranoid
If you want to make your Rails app feel like an object has been deleted but actually keep the data intact, you can use the paranoia gem to soft delete objects.
By default, this adds a timestamp into a
deleted_at attribute. Trying to lookup or access a record with
deleted_at set won’t work unless you write specific code. This essentially deletes the record without actually deleting the data.
In a recent project, I had to find all the objects of one Model that had been deleted, but who had a relationship with another object that wasn’t deleted.
It turns out paranoia gives us this for free!
Lets imagine two models,
class Post < ActiveRecord::Base acts_as_paranoid has_many :comments end class Comment < ActiveRecord::Base acts_as_paranoid belongs_to :post end
If we want to see deleted comments, but only ones that were attached to non-deleted posts, we can do the following.
Comment.only_deleted brings back only deleted items (
only_deleted is given to us through the paranoia gem).
Posts also use the paranoia gem, chaining them into our call with a
joins automatically gives us what we want!
For any ActiveRecord query we can call
to_sql to see what it is generating under the hood.
Comment.only_deleted.joins(:post).to_sql gives us;
SELECT "comments".* FROM "comments" INNER JOIN "posts" ON "posts"."deleted_at" IS NULL AND "posts"."id" = "comments"."post_id" WHERE "comments"."deleted_at" IS NOT NULL
comments.deleted_at IS NOT NULL (has been deleted) but
posts.deleted_at IS NULL (has not been deleted).
This is incredibly handy!